This invention relates to aqueous inks for ink jet printers, and more particularly, to aqueous ink jet inks containing hydrosols as additives to improve smear resistance of the ink.
Ink jet printing is a non-impact printing process in which droplets of ink are deposited on a substrate such as paper or transparency film in response to an electronic signal. Low cost and high quality of the output, combined with relatively noise free operation, have made ink jet printers a popular option to other types of printers used with computers. Both dyes and pigments have been used as ink colorants for ink jet printers. The dye-based inks while in general superior in color properties, have several disadvantages as compared to pigment based inks. The dyes are usually water soluble and remain so after drying on the substrate. They are easily redissolved by water spills, and the image smears on contact with felt pen markers. In addition, the dyes exhibit poor light stability relative to pigments and are known to fade even under office lighting. Thus, dye-based inks are often unsuitable for use in applications requiring moisture resistance and greater light stability. The pigments are preferred colorants provided the pigment dispersion can be made resistant to flocculation and settling.
Polymeric additives may be added to the pigmented inks to further improve their resistance to smear/smudge or general handling. However, such additives have a great tendency towards generating problems for the ink jet printing process. The most common ones include 1). aggravating the pigment dispersion stability; 2). building up solids around the nozzle plate resulting in misdirection of the ink drop or complete blockage of the ink delivery; and 3). interfering with the ink drop generation, especially in the bubble formation in a thermal ink jet device.
There exists a need for ink jet inks which have good water resistance and smear fastness. In particular, with pigment based inks there is a need to maintain the stability of the dispersion and pen reliability while improving water and smear fastness.